1. Field of the Invention
This invention relates to an image reading apparatus and an image reading method which use line sensors.
2. Description of the Related Art
An image reading apparatus and an image reading method which use line sensors to read images are well known. For instance, an image reading apparatus uses three line CCD (Charged-Coupled Device) sensors provided with red (R), green (G), and blue (B) filters respectively to generate RGB signals, thereby reading a color image. The apparatus generates a monochrome image by using the read RGB signals. Therefore, as for the starting position to read an image, the apparatus can start to read the image from the same place, taking no account of whether the image is a color image or a monochrome image.
Another known image reading apparatus has three color line CCD sensors provided with red (R), green (G), and blue (B) filters respectively and a monochrome line CCD sensor with no color filter. The color line CCD sensors are composed of physically different members from that of the monochrome line CCD sensor. These sensors are separated by a specific distance in the apparatus. Therefore, when an image is read from a document, it is necessary to change the starting position of image reading for each of the line sensors according to the reading mode. Since the starting position of image reading differs as described above, this apparatus, unlike the above apparatus, requires complex control in reading images, which results in a control load on the apparatus.
Therefore, there has been a need for an image reading apparatus and an image reading method which are capable of reducing the control load when the color line CCD sensors and the monochrome line CCD sensor are used to read images.